Thermally sensitive means exhibiting a continuous or stepless change in resistance, such as thermistors, have been used for controlling the gate signal to a power switch.
A thermally sensitive switch, such as a temperature sensitive thyristor exhibiting a true, abrupt switching characteristic, has been used to shunt the gate of a power switch in response to external heating of the thyristor by a load.
Such devices do not necessarily protect the power switch from thermal breakdown, with the resultant disadvantage of loss of gate control if the load does not thermally trigger the thyristor or thermistor before thermal breakover of the power switch, whereby the power switch loses its blocking ability thereby defeating its protective purpose.
Furthermore, such devices have only been used in discrete circuit form.